1. There are two parts to this examination. Each will take about 90
minutes.

2. There are 3 questions in Part I. You may refer to your course reader,
course notes, course handouts, and homework assignments.

3. Please write legibly and compose your answers so that you say what
you mean.

4. If you finish Part I early, you may leave the room and relax until
Part II begins around 5 P.M.

5. P.S. Don't forget to put your name on your blue book.

GOOD LUCK

Part I (75 Points)
Individual work. Write your answers in the bluebooks provided.

1. Sometimes science
is taught and learned as a collection of incontrovertible facts as I if
knowing about the natural world applied only to multiple choice tests where
every question had a single correct answer. While there is a body of knowledge
in science that we feel is certain, the process of discovery in science
is driven by uncertainty and the questioning of things thought to be certain.
(If one knew the answer, there would be no point in doing an experiment.)
The importance of scientific knowledge and understanding is that it helps
people evaluate situations, make reasonable predictions, and then make
better decisions in the face of uncertainty. Thus uncertainty is very much
a part of science both in the discovery and in the use of scientific knowledge.

You have read and discussed
in your group the article published in 1954 by Dr. Anthony Allison. Its
conclusions appear in virtually every biology textbook. Answer the following
questions relating to Allison's experiment and what he knew and didn't
know.

A. (5 Points) State
clearly
and concisely the hypothesis Dr. Allison was testing?

B. (20 Points) What
facts and observations did Allison know that contributed to the design
of his experiments? Divide your answer into two columns. On the left, list
those facts and observations (4 or more) that Allison knew. In the second
column, opposite each entry, indicate briefly how each contributed to the
design of his experiment.

C. (10 Points) Allison
probably designed and conducted his experiments without formal approval
by an independent human subjects review board. If you were to serve on
such a board, specifically what would you like to know, that was not addressed
in Allison's article, before considering whether or not to approve such
an experiment today? How would this information help you make a better
decision?

2. Pauling et al.
(1949) demonstrated that persons with sickle cell disease have a chemically
distinct hemoglobin (HbS). A few years later, Ingram identified the difference
between HbS and HbA as the replacement of valine for glutamic acid at position
6 of the beta-chain. Subsequently, hundreds of other variant human hemoglobins
have been discovered and characterized. Usually the variants differ from
HbA by a single amino acid replacement in the alpha or beta-chain.

A. (15 Points) Consider
a man who is heterozygous for a mutation affecting his hemoglobin such
that HbA and "HbX" are observed. HbX has the same electrophoretic mobility
as HbS but does not cause red blood cells to sickle at low oxygen tension.
His wife has sickle cell trait. Upon examining the electrophoretic pattern
of hemoglobin from their second child, you conclude that HbX results from
a mutation affecting the alpha-chain, not the beta-chain. Draw and clearly
label a diagram showing the electrophoretic patterns for both parents and
the second child. Explain and show how these observations would differ
if the mutation affected the alpha-chain.

B. (10 Points) Human
HbA contains 12 sulfur atoms and 4 iron atoms for a S to Fe ratio of 3
to 1. How could it be possible for someone in this class to have a hemoglobin
with a S to Fe stoichiometry of 11:4 or 13:4? No credit without an explanation
that shows a clear understanding.

3. Answer one
of the following two questions based on quotations from Stokes's 1864 article.

A. (15 Points)
"Very different is the effect of carbonic acid.... I took two portions
of defibrinated blood; to one I added a little of the reducing iron solution,
and passed carbonic acid into the other, and then compared them. They were
as nearly as possible alike. We must not attribute these apparently identical
changes to two totally different causes if one will suffice."

Clearly carbonic acid is
not a reducing agent. Can you attribute conceptually the "apparently identical
changes" to a single process?

Or

B. (15 Points) "When
the watery extract from blood clots is left aside in a corked bottle, or
even in a tall narrow vessel open at the top, it presently changes in colour
from a bright red to a dark red, decidedly purple in small thickness....
The tint agrees with that of purple cruorine obtained immediately by reducing
agents.... On shaking the solution with air it immediately becomes bright
red, and now presents the characteristics of scarlet cruorine."

Explain Stokes's observations
in terms of our current understanding of the chemistry of hemoglobin.

Part II Group work (25 Points) If
your group cannot come to consensus, dissenting members may submit a separate
answer for separate grading.

On March 21 of this year, the day of your
midterm examination, the journal Nature published a paper about
hemoglobin and nitric oxide that caused quite a stir.(1)
National Public Radio had a program about it and the New York Times described
the discovery in a prominent article. Who would have thought that hemoglobin
had not yet yielded all of its structural and functional secrets after
more than a century of intense study by thousands of researchers?

Nitric oxide (NO), like CO and O2,
reacts with the iron in the heme group of hemoglobin (Hb). When NO reacts
with oxyhemoglobin (HbO2), methemoglobin (metHb) and nitrate
form. This chemistry was known in the 1920's at a time when NO was thought
to be an inorganic molecule of no biological significance except as a poison
akin to CO. Within the past decade, NO became recognized as a very potent
vasodilator and messenger molecule(2) and
was named "Molecule of the Year" by Science magazine in 1992.(3)
It is involved in activities as diverse as regulation of blood pressure,
male erection, and neurotransmission. The plot thickened in March when
it was shown that NO in the form of S-nitrosothiols such as S-nitrosoglutathione
(G-SNO) transfers its NO group to the reactive sulfur of cysteine 93 on
the -chain of hemoglobin to form S-nitrosohemoglobin (Hb-SNO). These S-nitrosothiols
do not react with heme iron the way free NO does. In fact, the nitrosylation
of Cys 93 occurs more readily with HbO2 than with Hb and does
not form metHb. Conversely, S-nitroso-deoxyhemoglobin transfers NO back
to glutathione (GSH), a tripeptide, more rapidly than does S-nitroso-oxyhemoglobin.
The fact that hemoglobin in arterial blood is nitrosylated while in venous
blood it is not suggests that these reactions are physiologically important
and that the NO is produced by the lungs and distributed throughout the
body by hemoglobin.

One goals of the CHEM-342 is to encourage
you to think chemically about biological systems. Another goal is
to be able to apply what you know to new situations. Prepare a diagram
(model) that would serve as a figure to illustrate the preceding paragraph.
[Note: There is no single right answer. Models will be evaluated and graded
on their informativeness, simplicity, clarity of presentation, inclusion
of important information, creativity, and lack of extraneous details or
misinformation. Please, nothing PG or X-Rated.]